Enhanced Protective Performance of Carbon Nanotube-Reinforced Waterborne Epoxy Zinc-Rich Coatings for Corrosion Protection of Steel Structures

Carbon nanotube-reinforced waterborne epoxy zinc-rich coatings were developed by modifying waterborne epoxy zinc-rich formulations with varying amounts of carbon nanotubes (CNTs), to improve the coatings’ corrosion resistance and their protection for Q355b steel in environments rich in chlorides. A detailed investigation of the microstructural changes in the coatings prior to and following corrosion was conducted through FTIR, SEM, XRD, and XPS analytical techniques. The effectiveness of these innovative coatings in providing corrosion protection for Q355b steel in chloride conditions was assessed via electrochemical corrosion methodologies and neutral salt spray testing. The results indicate that an increase in the CNT concentration led to an initial enhancement in the corrosion resistance of the coatings, followed by a decrease, with optimal performance noted at 0.3 wt.% CNTs. During the electrochemical evaluations, the open circuit potential (OCP) of the coating containing 0.3 wt.% CNTs remained stable below the critical threshold of −0.78 V for an extended period, indicating sustained cathodic protection. In comparison to the coatings with CNT concentrations (wt.%) of 0.1, 0.5, 0.7, and 1.0, the coating with 0.3 wt.% CNTs demonstrated the lowest corrosion current density, measured at 0.0322 µA/cm2. Further validation of its exceptional corrosion resistance was provided by the 240 h neutral salt spray tests. This performance can be linked to the capability of the CNTs to improve electrical conductive connectivity between the zinc particles and the Q355b steel substrate beneath them, subsequently enhancing both the cathodic protection of the coating and its physical shielding effectiveness.